Q4 — Explain: Group 1 reactivity (4 marks)

Question: Explain why the reactivity of the alkali metals (Group 1) increases going down the group from lithium to caesium.

Mark scheme (4 marks — indicative content):

• Group 1 atoms have one electron in their outer shell (1).
• Reactivity depends on how easily this outer electron is lost to form a +1 ion (1).
• Going down the group, atoms have more electron shells, so the outer electron is further from the nucleus (1).
• Increased shielding by inner shells reduces the effective nuclear attraction on the outer electron (1).
• Therefore the outer electron is lost more easily further down the group, so reactivity increases (1).

Award up to 4 marks. Must reference shells/distance AND shielding for full marks at Grade 9.